Hydraulic press

ABSTRACT

A press having a vertical reciprocating ram actuated mechanically and hydraulically to advance the head thereof. A hydraulic thrusting unit for actuating the ram, removable from the body and comprising a unitary assembly.

PATENTEUJUL 4 I972 INVENTOR. PHILIP E. ASHTON ATTORNEY PATENTEDJUL 4 m2 3.673 .600

' SHEET 3 or 7 INVENTOR. PHILIP E. ASHTON (ATTORNEY PATENTEnJuL' 4 I972 saw u or 7 INVENTOR. PHILIP E. ASHTON ATT RNEY PATENTEDJUL "4 I972 SHEET 6 OF 7 INVENTOR. PHILIP E. ASHTON ATT RNEY PATENTEUJUL" 4 m2 SHEET 7 BF 7 INVENTOR. PHILIP E. ASHTON HYDRAULIC PRIBS This invention relates to improvements in thrusting devices having a thrusting member actuated by combination of mechanical and hydraulic forces. In particular, it relates to devices such as are shown in US. Pat. No. 2,774,217.

The prior art structures have been difficult to maintain and repair in the field and the slightest rnal-function of the valves has necessitated withdrawal from use and complete dismantling. They have also, because of their welded mono bloc construction been awkward to manufacture and very expensive to modify to the differing needs of various users. Additionally, they afforded no thrust limiting means and lacked any way of preventing the ram and attached tools from descending under the influence of gravity.

Accordingly, the objects of the present invention include (a) a thrusting unit which may be readily secured to a variety of supporting structures without change in its design and which can be quickly and easily replaced on its support by another unit with minimal down time; (b) a hydraulic thruster in which the various valves, with their seats and seals comprise complete units that can be removed and replaced without dismantling the thruster as a whole even draining the operating fluid and wherein all wearing parts may be replaced without machining, brazing or welding, etc.; (c) the provision of an improved piston construction suitable for use at relative-' ly high pressures approximately 5000 p.s.i.) and which (i) tends to counteract side thrust and centers itself in the cylinder, (ii) need not be made with the customary close fits and tolerances, (iii) affords easily renewable non-metallic wearing parts, (iv) prevents oring pinch or extrusion, (v) may include a multi-element packing of the oring type without incurring the customary inter-packing pressure trap; (d) the provision of a pressure limiting device that is easily adjustable without the use of tools, affords good repeatability of settings and which may be eliminated from or added to a thrusting unit by the simple exchange of parts without fuss or complicated adjustments; (e) a thrusting unit of the type in case needing no brazing, welding or other permanent fastening for assembly of its major components; (f) the provision of a simple means of automatically spilling hydraulic pressure where there is an attempt to traverse the ram beyond its designed stroke limit; (g) the provision of a thrusting unit of the type in case where any worn part may be exchanged for a new one without machining and by using only simple hand tools.

How these and other objects not specifically mentioned are attained may be discovered from the following specification and claims and the appended drawings of which:

FIG. 1 is a sectional elevation of a thrusting unit as viewed from the line 1-1 ofFIG. 3 or FIG. 8;

FIG. 2 is an elevation, partly in section and partly broken away, of the unit as viewed from the line 2-2 of FIG. 1 or FIG. 9;

FIG. 3 is a fragmentary plan view of the unit in case;

FIG. 4 is a plan view of the unit with cover and star wheel removed;

FIG. 5 is a bottom view of the unit as seen from the line 5- 5 of FIG. 2;

FIG. 6 is a sectional view of the unit as seen from the line 6-6 of FIG. 2;

FIG. 7 is a sectional view of the unit as seen from the line 7-7 of FIG. 2;

FIG. 8 is a front elevation, on a reduced scale, of a thrusting unit carried in a frame and constituting a bench press;

FIG. 9 is a side elevation of the device of FIG. 8;

FIG. 10 is a plan view on an enlarged scale of a portion of the valve mechanism shown in FIG. 4;

FIG. 11 is a sectional elevation of the structure shown in FIG. 10 as seen from the line 11-11 thereof and including portions of other parts;

FIG. 12 is similar to Fig. 11 but taken on the line 12-12 of FIG. 10;

FIG. 13 is a fragmentary section of the ram guide embodied in FIG. 1 but modified to incorporate a frictional device;

FIGS. 14, 15 and 16 are fragmentary sections, on an enlarged scale, of modifications of the piston packaging shown in FIG. 1;

FIG. 17 is a copy, on an enlarged scale, of the sectional view of main valve as seen in FIG. 2.

Throughout the drawings, like numbers indicate like parts.

Referring to the drawings which show a preferred embodiment of the invention, attention is first directed to FIGS. 8 and 9 depicting a hand operated thrusting unit 20, mounted in a frame 21 and having a vertically reciprocable ram 22. The said frame comprises a thrust opposing bed-plate 23, side plates 24 and unit carrier 25, the whole forming what is a substantially C-shaped bench press structure 26. Rotation of star wheel 27 in a CCW (counter-clockwise) direction (see arrow in FIG. 9) advances ram 22 toward said bed-plate and rotation in the opposite direction will retract it. Such advance is first caused by mechanical means comparable to the mechanism of an ordinary arbor press and then, after the thrust load attains a predetermined value, hydraulic means are automatically brought into operation to augment said thrust: adjustable means are provided to limit the total thrust which may be applied by said ram. Unit carrier 25 affords a clamp 28 having a strap 29 held by screws 30; the said clamp is internally threaded, as indicated at 31 for engagement with the thread 32 at the lower end of tubular housing 33 (see FIGS. 1 and 2) so that when screws 30 are tightened, the unit 20 is rigidly secured to the frame 21. A strut 34 is secured to unit carrier 25 and has a palm 35 supporting and very slightly encircling the said unit; a metallic band 36 held by screw 37 completes such encirclement in the ordinary manner. A clearance between strap 29 and said unit carrier forms a keyway as indicated at 38 to receive an ordinary Woodruff key 39 seated in key seat 40 in ram guide 41 (see FIG. 2); this expedient affords accurate angular location for unit 20 relative to the frame 21.

Considering next the thrusting unit 20, as detailed in FIGS. 1-7 inclusive, the said unit comprises a tubular housing 33 having an external thread 32 at its lower end for anchorage, as above explained, in a cooperating supporting structure. The other end of said housing has an internal thread 43, engaged by an external thread on cylinder head retainer 44. The said retainer has abutting engagement with cylinder head 45 which is a slip fit in housing 33. The said housing is shaped to aflord an internal shoulder 46, that serves to position and support cylinder carrier 47, which is a thick metallic disc snuggly fitted inside the housing and is forced out as at 48 and 49, to afford close support to pump cylinder 50 and thrust cylinder 51 respectively and hold them in good working alignment. The said cylinders extend from abutting shoulders 52 and 53, in the said carrier, to cylinder head 45 where they enter suitable grooves 54 and 55 and have sealing compressive engagement with O-ring gaskets 56 and 57. The upper edge of said cylinder head is formed as at 42 to afford lodgement for an O-ring gasket 58, which, when slightly flattened by the retainer 44, seals the space above said cylinder head and affords a reservoir 59 for working fluid (not shown). The lower end of housing 34 is internally machined to give snug support to ram guide 41; two studs 60 are screw-threaded into cylinder carrier 47, extend through the said guide and, by means of nuts 61, hold it tightly in place with its flange 62 abutting the end of said housing. As mentioned in relation to FIG. 8, a key seat 40 may be cut in guide 41 and the housing 33 will be slotted as at 63, permitting key 39 to project for placement in key way 38. The ram 22 is supported in and passes through its guide 41; at its upper end, it has a thrust piston 64, which is a sealed sliding fit in the thrust cylinder 51 and will later be described in detail. At its lower end, said ram has a co-axial hole 65 for receipt of a tool shank or the like which may be clamped in place by a suitable screw threaded into tapped hole 66; a cross drilling 67 affords access to such shank by a knock-out bar or wedge (not shown).

A gear carrier 68 is supported by and slidable on ram 22 and is also slidable on guide bar 69, which is supported at its upper end by cylinder carrier 47, and at its lower end has an enlarged cylindrical portion 70 that is retained in ram guide 41 by a screw 71 and washer 72. Removal of said screw and washer permits said guide bar to be withdrawn downwardly through said ram guide. Gear shaft 73 is rotatably supported in gear carrier bars 74, and a one end carries, in keyed engagement, star wheel 27 which is retained by screw 75; at the other end is rigidly secured a gear 76, having teeth 77, in engagement with teeth 78, cut in said ram; said bars and said shafl protrude out through the elongated hole 79 in tubular housing 33. Torque applied to said star wheel in the direction indicated by the arrow in FIG. 9 will tend to cause said gear carrier to clirnp up said ram and simultaneously tend to move the latter downwardly.

In order to exert a mechanical thrusting effort by said ram, it is necessary to restrain the upward motion of gear carrier 68. This is done by a latching device comprising a plate or tongue 80 secured to the underside of said gear carrier and formed with a bevelled upper face 81, shaped'for engagement with the bevelled end 82 of the notch 83, in latch finger 84. The said finger is pivoted on pin 85 and extends downwardly through a square clearance hole 86 in ram guide 41 for manipulation in case of need and has a hole 87 for engagement with a pin or tommy bar for that purpose. A compression spring 88, cooperating with plunger 89, is carried in a horizontal hole 90, in said ram guide and urges the top of said finger toward said tongue. With gear carrier 68 in its lowest position,

there is a gap between the bevelled surfaces 81 and 82, as is clearly shown in FIG. 2. This gap, when star wheel 27 is turned to cause descent of said ram, allows said gear carrier to climb upwards until stopped by said bevelled faces engaging each other, the ram will then move downward by simple mechanical operation. If the ram meets an obstacle to its descent, the application of sufiicient torque to said star wheel will cause the latch to be sprung open by interaction of said bevelled faces 81 and 82 and leave the gear carrier 68 free to ascend the ram; the function of the play allowed by the gap in the latch concerns valve operation and will later be described fully, It may be noted that the tip of latch finger 84 has a second bevelled face 91 whereby the tongue 80 may force said finger aside when said gear carrier descends to its lowest position.

A piston 92, having a sealing packing 93, is reciprocable in pump cylinder 50, it has a rod portion 94 that its lower end 95 is reduced in diameter to form a thrust shoulder 96 and also to fit in a hole 97, in gear carrier 68, where it is retained by a suitable pin 98. Movement of the gear carrier up and down ram 22 will similarly move said piston in cylinder 50 and thereby pump working fluid from reservoir 59 into thrust cylinder 51 to urge said ram downward. The valve mechanisms involved in this action comprise (a) a pumping valve unit 99, directing fluid from said reservoir to pump cylinder 50 and thrust cylinder 51; (b) a so-called main valve" unit 100 controlling the direct flow of fluid in either direction between said reservoir and said thrust cylinder, as called for by operating conditions; (c) an adjustable pressure (and consequently thrust) limiting valve unit 101, carried by and preferably forming part of said pumping valve unit.

Pumping valve unit 99 is positioned on cylinder head 45 by screw 102 and dowel 103, which pass through cover plate 104, body 105 and into said cylinder head. Body 105 is shaped to afi'ord an inlet valve comprising inlet passage 106, valve ball 107 supported on seat 108 and opening on to a port 109, in the said cylinder head, which leads to pump cylinder 50. Additionally, said body affords a delivery valve comprising delivery pasage 110, valve ball 111 supported by seat 112 and then leading to a second port 113 in the cylinder head which gives access to thrust cylinder 51. O-ring gaskets 114 are located at the termini of the various passages as shown in FIGS. 11 and 12 where by sealingly engage said cylinder head and said cover plate to preserve the integrity of the passages described. The main valve unit 100 is held in place by a pair of screws 1 which pass through body 116 into said cylinder head. Said body has a cylindrical port 117 that communicates with reservoir 59 via drillings 118; it is also grooved for O-ring gasket 120, and is suitably finished on its underside to afford a seat for main valve 121. Said main valve is actually a compound device; it has a head 122 which preferably incorporates a nylon sealing ring 123 and has a hollow stern 12A, slidingly supported by and protruding through said body and having a cross drilling 125 near said head. A small pilot valve 126 is carried by said main valve, it has a shank 127, slidable in said stem and has a head 128, formed for sealing seating in the flaring mouth 129 of the passage 130 through said stern. A collar 131 is secured to the other end of said shank and a light compression spring 132 is carried on said hollow stem in abutting contact with said collar and the bars 133; by this arrangement, a simple spring serves to hold both valves on their seats. 'lhe said shank has a short reduced diameter portion 134 directly behind head 128 which allows the flow of fluid from thrust cylinder 51 through chamber 135, hollow stern 124, port 117 and drillings 110, into said reservoir when said pilot valve is opened prior to unseating said main valve. This makes it possible to spill high pressures, approximately 4000 or 5000 p.s.i., with little efiort and to then open the main valve for egress of fluid from said thrust cylinder to said reservoir when it is desired to move ram 22 upward. The spring 132 is proportioned to allow the main valve to open by suction when the ram is mechanically moved downward. It is convenient to point out here that the clearance between collar 131 and valve stem 124 need only be quite small to allow a pressure spill and that the major portion of the travel of said collar is available for opening said main valve. How the main valve is opened will be explained later.

Turning next to the pressure limiting valve unit 101 which is preferably manually adjustable to any thrust effort limit between zero and the thrusting unit's maximum capability, the unit is not essential and may be replaced by a blank cover plate for valve body 105 if desired. It ha, however, great utility in some repetitive operations such as compacting powder metal blanks, spring testing, etc. The unit 101 comprises a spill valve ball 136 supported on seat 137 and controlling spill passage 138 in cover plate 104 and which has communication with thrust cylinder 51 through passages 1 10 and 113. A lever 139 has a pin 140 that presses said ball to its seat, said lever is loosely carried by a stud 141 secured to said cover plate and is restrained by pin 142 serving as a fulcrum. The other end of said lever is urged downwardly by a compression spring 143 in threaded engagement with a pair of end pieces 144 that are a slip fit on adjusting screw 145. Said screw passes through a clearance hole 146 in said lever. lt is split axially at its lower end 147 and slightly distorted to provide a snug shake-free fit in threaded hole 148 in said cover plate; the friction so engendered prevents unwanted movement of said screw during operation. A disc having a projecting lug 149 abuts the upper end piece 144 and is firmly secured to said screw, whose rotation will cause its axial movement and, depending on direction, increase or reduce the load imposed by pin 140 on valve ball 136 by varying the loading of spring 143 which thereby governs the thrust controlling function of valve unit 101. The are through which screw may be turned is limited by the engagement of lug 149 with one side or the other of housing cover hold-down stud 150. Rotation of said screw is affected by manual manipulation of the ribbed knob 151, which has an index arrow 152 and may be set at any point between the zero and eight tonnage value numerals stamped in housing cover 153. Said knob has a hub 154, carried in bearing 155 and sealed against fluid leakage by O-ring seal 156 while a snap ring 157 carried in a suitable groove serves as a retainer. Said hub is made hollow to receive the upper end of screw 145 and has a keyway 158 to aflord axially slidable engagement with pin 159 anchored in said screw. The said housing cover is held down by a nut 160 and stud 150 which is threaded into cylinder head 45 and passes through clearance holes 161 and 162 in lever 139 and plate 104 respectively. An O-ring gasket 163 seals the joint between cover 153 and the top of housing 34; an air vent or breather 223 is provided in said cover, it comprises a resilient washer 164, a back-up washer 165, and a screw 166, threaded into said cover and its loss is prevented by a stop nut 167. As shown, the breather is open affording atmospheric access to reservoir 59 through port 168. When said screw is tightened down, the said ports are closed by said resilient washer and the thrusting unit 20 may be placed in any position without loss of working fluid. Attention is drawn to the fact that as spring 143 is carried by threading it on to end pieces 1441, its active length and, therefore, its effective rate is easily adjusted so that valve spill pressures may conform to the tonnage markings on said cover.

Turning next to operation and control, valve operating lever 169, located in reservoir 59, is held loosely at one end under the head of screw 170, by a compression spring 171; a tubular spacer 172 is carried on said screw and determines its height from cylinder head 45, into which it is threaded. Said lever has a hole 173, afl'ording clearance for stud 150; it is drilled and tapped for screw 174, positioned over valve shank 127 and held against unwanted rotation by compression spring 175. The other end of said lever has a slot 176, to accommodate full rod 177, which is threaded at the upper end and carries a nut 178 bearing a washer 179 shaped to allow rocking of the lever. Said pull rod passes down through a suitable hole in cylinder head 45, its exit from remrvoir 59 being sealed by an O-ring 130 held in place by a washer 181 and a compression spring 182 pressing on said washer and urging said lever and pull rod upwardly. Said lever and pull rod are shown, in FIG. 2, in their lowest positions where the screw 174 is holding main valve 121 and pilot valve 126 in their open positions. Said pull rod passes on through a clearance hole in cylinder carrier 47 and a similar hole 190 in valve tripper 183 and freely within tripper tube 184, through lug 185 on gear carrier 68, it is threaded at its lower end and has there a nut and washer 186 and 187 respectively; said tripper tube is a free sliding fit on said lug and rests on said washer; apart from its embracement by O-ring 180, pull rod 177 is free floating between lever 169 and the under side of lug 185. Valve tripper 183 is located in a groove 188 in the under side of cylinder carrier 47 and at one end is loosely held on a shoulder screw 189 while the other end has the earlier mentioned clearance hole 190 and rests loosely on tripper tube 184 as shown in FIG. 2. Said tripper carries an upwardly projecting pin 191 that protrudes into the path of thrust piston 64 near the bottom of its extreme possible stroke. The parts are so proportioned that, should said piston press said pin and tripper downward, the resulting motion of said tripper tube, bearing on washer 187, will carry pull rod 177 into the position shown in the drawing, and in so doing, open the main valve, thus preventing said thrust piston being forced by hydraulic pressure into damaging contact with shoulder 53.

If, with the parts in the positions shown in the drawing, star wheel 27 is turned counter-clockwise, the gear carrier 68 will climb up ram 22 until the gap between tongue 80 and the end face 82 of notch 83 is closed and carrier movement stopped. The limited upward climb of said carrier so permitted will be sufiicient to lift lug 185 away from washer 187, thus allowing spring 182 to move pull rod 177, tripper tube 184, tripper 183 and valve operating lever 169 upward and allow main valve 121 and pilot valve 126 to be closed by spring 132. The upward movement of the pull rod will be arrested by said tripper coming into contact with the bottom of groove 188 in cylinder carrier 47. Continued rotation of said star wheel will next overcome friction in said ram and the thrust piston and move them downward when, as said piston descends it will draw fluid from reservoir 59 through the main valve unit and into the thrust cylinder. 1f the ram now meets a firm obstacle, the latch will be forced open as earlier described, whereon the gear carrier will continue its climb up the ram and carry pump piston 92 with it, thereby forcing fluid from pump cylinder 50, through pumping valve unit 98 and into thrust cylinder 51 so as to augment the thrust reaction of gear 76 on ram teeth 78. Turning the star wheel backward (clockwise) will cause the gear carrier to descend when the pump piston will draw more fluid from the reservoir through the pumping valve unit and into said pump cylinder. The pumping action just described may be continued by oscillating the star wheel to cause reciprocation of said pump piston. Termination of pumping may, depending on the type of obstacle encountered by the ram, leave the device under hydraulic pressure where it may remain as long as desired. Rotation of the star wheel clockwise as to carry the gear carrier down to its lowest point will reengage the latch and by drawing the pull rod down, reopen the main valve and release all fluid pressure. The relationship between pump and thrust piston areas will govern the hydraulic thrust augmentation. In practice, a ratio of 8 or 10:1 has been satisfactory which, with a suitable selection of gear and star wheel diameters can conveniently make an overall advantage of or even :1 quite practical.

When the thrusting unit 20 is oriented vertically, friction is substantially the only influence countering the effects of gravity on ram 22; suction cannot be relied on because of the valve arrangements. In most cases, the piston packing friction is adequate, but when heavy tools are attached to the ram, additional means may be needed to prevent it dropping. One such means is shown in FIG. 13, where ram guide 41' is similar in all respects to the ram guide 41 (see FIG. 1) except that an angular slot 192 is formed to freely house the obtusely angled wedge 193 that is urged into contact with ram 22, by the effects of compression spring 194 and the load adjusting screw 195. Friction between the wedge and the ram tends to prevent the latter dropping and the effect of the angle of face 195 adds to that tendency, but when the ram is moved upward, the effect of said angle is reversed and it afiords some relief from such friction. The drawing shows only a single wedge but it is obvious that a plurality of them or even a full ring can be used as desired.

As the machine here described is a single acting device with open ended cylinders working over a wide pressure range, the quality of the seals on both pump and thrust pistons is important. Also it is very desirable to prevent side-loads which may be imposed on the ram from forcing the thrust piston into contact with the cylinder wall. Attention is now drawn to FIG. 1. Thrust piston 64 is secured in any convenient manner to ram 22, and preferably has a wiper ring 197 of felt or other suitable material, carried in a groove 198. The piston packing components are located above said wiper ring on a reduced diameter portion 199 that extends upward from a sloping shoulder 200. Above said portion, the piston is shaped to carry a spring snap ring 201, serving with guard ring 202 to retain the packing components in place. Said components comprise a wear ring 203 and a conventional elastomeric O-ring 204, squeeze fitted in the usual manner between said portion and the inner wall of cylinder 5 I. Said wear ring is preferably made of a fairly hard, tough and somewhat elastic or flexible synthetic material with a low coefiicient of friction, such as nylon in a formulation suitable for hearings or gears, for example: an enlarged cross-sectional view as given in FIG. 14 which clearly shows the details of its shape. The sloping shoulder 200 is preferably polished and the lower face 205 of wear ring 203 is shaped to sit thereon; the upper face of said wear ring affords a channel with sides or flanges 206 and 207 that partially nest the O-ring 2M. Said wear ring is sized so that its outer diameter is a slight interference fit in cylinder 51 and the minor diameter of flange 207 is a slight interference fit on reduced portion 199 while the remaining inner surface 208 clears said portion. When installed, the friction of the interference fit of the wear ring on said cylinder wall may be made sufficient to prevent ram 22'from falling of its own weight and also to prevent O-ring extrusion; extrusion is also prevented by the interference fit of said flange on said reduced portion. Said flange is then enough to be deformed by the diametrical changes caused by said interference fits while the clearance between said inner surface 208 and said reduced portion makes radially inward compression possible. When under fluid pressure, said wear ring is forced downward in to said sloping shoulder 200 and so exerts a centering force on piston 64; this effect also enhances the anti-extrusion function of said wear ring. The foregoing construction makes it possible to allow an unusually large clearance between said piston and its cylinder wall and obviates any metal to metal contact between them. The arrangement of packing 93 on pump piston 92 is similar, except for size to that above described and is therefore not detailed.

The packing shown in FIG. 15 is generally similar to that of FIG. 14 except that the wear ring 209 is of simple trapezoidal cross section and that the function of flange 207 is served by inner ring 210 which is preferably a slight interference fit on portion 199. Under fluid pressure, said wear ring affords the centering and anti-extrusion functions previously described while inner ring 210 serves by virture of its wedge-like bearing on ring 209, to aid in centering the piston, augmenting the anti-extrusion function of ring 209 and preventing O-ring extrusion at the inner diameter.

FIG. 16 shows two other wear ring constructions and also a novel tandem O-ring seal. Although shown together in one drawing for convenience, there is no necessary connection between the three items and the tandem seal could work equally well with or without wear rings. Turning to the wear ring arrangements, the upper construction has the earlier described snap ring 201, and guard ring 202 and a reduced diameter portion 199' which, however, rises from a square shoulder 21 1 on piston 215 and on which is carried the O-ring 204, a wear ring 212 having a flange 213, and an elastomeric back-up ring 214. The said wear ring has, as in the other cases, a slight interference fit in the cylinder, not shown, the back-up ring serving to reinforce the wear ring against radial collapse and simultaneously serving a piston centering function and extrusion of the O-ring behind the wear ring is prevented also. In the lower structure, the wear ring 215 is exactly like wear ring 203 except that it has no outer flange; which tends to simplify manufacture.

The tandem O-ring seal affords longer life than the ordinary single ring and largely insures against weepage if the thrusting unit is left under load for a protracted period. Here the piston 218 is bored out as at 216, and has a groove 217 of appreciable width in which is located an O-ring 204 functionally squeezed in the normal manner between the cylinderwall and the groove bottom 219; when ring 218 is not under fluid pressure, it is free to roll along said groove bottom 219. An elastomeric band 220 is a snug fit inside said bore and, covering a hole 221 which runs from the upper portion of said groove bottom to said bore, serves as a valve, permitting fluid to flow from said groove to said bore but not in the reverse direction. lfdesired, a reinforcing band 222 may be secured to band 221, narrow enough to be overlapped by the edges thereof while serving to prevent valve material being forced into said hole. In use, O-ring 218 will have no duty while ring 204 maintains its sealing function, but if there is leakage past the latter, the O-ring 218 will assume its duty as a seal. When pressure above the piston is reduced, any pressure build-up between the two O-rings will be relieved by fluid flow inward past valve 220. If the piston is moved downward by mechanical effort (i.e., not by fluid pressure), the rolling of O- ring 218 to the top of its groove will force any fluid thereby displaced, through said hole and past said valve.

From the foregoing, it will easily be seen that the construction disclosed constitutes a very appreciable advance over the prior art as the thrusting unit as a whole is easily removed from its mount, for servicing or replacement, if necessary, without having to transport a heavy and cumbersome structure. Also, the valves may be removed and replaced without disturbing any tools mounted on the unit or draining the working fluid. It is only necessary to remove cover 153 and valve operating lever 169 and thereafter the appropriate screws 102 or 115. In

those cases where a pressure limiting valve is not desired, a 7

blank cover plate (not shown) may be used on valve body 105 in place of cover plate 104, as has already been mentioned; in such case, the reservoir cover 158, would be replaced by a plain reservoir cover (not shown) although, of course, the breather 223 would still be desirable. In such case, a pressure gauge is frequently desirable and provision for connecting one is afforded by drillings 224 and 225 which lead from the interior of thrust cylinder 51 to the opening through a hole 226 in housing 33. As indicated in FIG. 1, screw threads are provided in drilling 225 to receive a suitable connecting fitting or, where appropriate, a simple pipe plug. If desired, the valve units may be combined in a simple block, but the arrangement shown appears most advantageous.

What is claimed is:

1. A thrust producing unit of the class described arranged and adapted for attachment to and removal from a support as an entity, said unit having a hollow housing containing at least in part:

a. a reservoir for operating fluid;

b. a cylinder head;

c. a pair of cylinders of dissimilar diameter each having one end in sealed engagement with said head at one side thereof;

d. a thrusting ram secured at one end to a piston slidable in the larger of said cylinders;

e. a guide afiording sliding support to said ram at a point remote from said piston;

f. power transmission means for transmitting energy from without said housing to impose a reciprocative force on said ram and being movable relative thereto by reaction to said force in the direction opposite thereto;

g. a pump comprising the smaller of said cylinders and a piston movable therein by movement of said transmission means to afi'ect a flow of fluid from said reservoir to the larger of said cylinders and impose a thrusting effort on said piston therein and thence to said ram;

h. pumping valve means comprising an inlet valve and a delivery valve for controlling said flow;

i. main valve means comprising a main valve seatable by fluid pressure and openable by suction to permit the flow of fluid into said larger cylinder from said reservoir and a spring biasing said main valve against the urging of suction;

j. releasable restraining means interposed between said housing and said transmission means to permit only limited movement thereof relative to said housing prior to release by said restraining means and permitting further movement thereof afler release thereby, said release being automatically affected when said reaction to said force reaches a predetermined value;

k. valve actuating means operable by movement of said transmission means to open said main valve aginst pressure and thereby permit the flow of fluid from said larger cylinder to said reservoir said actuating means comprising 1. a first link having a portion engageable with said main valve,

2. connecting means engaging said link and said transmission means and so proportioned that movement of said transmission means in one direction while within the range of said limited movement will cause said main valve to be opened while movement in the reverse direction within said range will permit said main valve to be closed,

3. a second link arranged to engage and move said connecting means in a valve opening direction only and having a portion extending into the path of said first mentioned piston for engagement thereby when near the extreme limit of its excursion away from said cylinder head whereby movement of said first mentioned piston beyond said point will cause fluid pressure thereon to be relieved by the opening of said valve;

1. a cylinder carrier supported by an inner surface of said housing and having supporting engagement with said cylinders;

m. a cylinder head retainer arranged and adapted to urge said cylinder head and said cylinders toward said carrier and to transmit hydraulically imposed thrust to said housing, said unit being characterized in that said transmission means may impart a direct mechanical thrust on said ram and by simultaneous reactive movement, may also by means of said pump and said first mentioned piston impose a hydraulic thrust on said ram.

2. The device according to claim 1 in which said housing comprises a tube having a configuration engageable by a mating configuration on a support for said unit, whereby reaction to thrust imposed by said ram on said support may be transmitted to said support.

3. The device according to claim 2 wherein said cylinder head retainer comprises a sleeve engaged with a surface of said tube and which in conjunction with said cylinder head comprises said reservoir.

4. The combination of a device according to claim 2 and a support therefor, said support comprising a thrust opposing surface and a unit carrying portion having a configuration for mating with said configuration on said unit.

5. The device according to claim 1 wherein said pumping valve means comprises a unit attached to said cylinder head and situated within said reservoir.

6. The device according to claim 1 wherein said main valve means comprises a unit attached to said cylinder head and located within said reservoir.

7. The device according to claim 1 which further comprises a pressure limiting valve means arranged and adapted to limit the hydraulic pressure that may be developed by said pump and thereby limit the thrust that may be imposed on said ram.

8. The device according to claim 7 wherein said pressure limiting valve means comprises a pressure limit adjusting means having a movable part movable to a desired setting from a point without said thrusting unit.

9. The device according to claim 8 wherein said pressure limiting valve means further comprises a support for said movable part of said adjusting means and said adjusting means further comprises a portion for imposing the bias of a resilient member on to a valve openable by hydraulic pressure for pressing said valve to a closed position on a seat until said hydraulic pressure reaches a predetermined value.

10. The device according to claim 9 wherein said movable part comprises a portion shaped for manipulation and which further comprises a screw threaded member rotatable by said portion shaped for manipulation and arranged to vary the bias imposed by said resilient means according to said predetermined value.

ll. The device according to claim 10 wherein a. a cover carried on said pumping valve means has an orifice communicating with a fluid conducting passage therein and affording said valve seat;

a link movably attached to said cover afiords said portion for imposing said bias and engages said resilient means to receive the bias thereof for urging said valve to a closed position on said seat;

c. a closure for said reservoir afi'ords said support and has markings indicative of predetermined values relative to which said protion shaped for manipulation may be indicatingly moved;

said screw threaded member engages said cover, affords a reaction point for the bias of said resilient member, affords a frictional bearing surface and has an interlocking engagement with said portion shaped for manipulation arranged and adapted to permit said closure and said last mentioned portion to be removed from said unit and said screw threaded member and to be replaced thereon without falsification of the value of said markings.

12. The device according to claim 1 wherein said releasable restraining means comprises a latch finger which a. is carried in movable relationship by said guide;

b. afi'ords its latching function within said housing;

c. is accessible from without said housing for non-automatic unlatching manipulation.

13. The device according to claim 1 comprising a friction creating component carried by said guide; and arranged to impose a frictional force on said ram by virtue of a wedging action between said guide and said ram, to prevent free fall thereof, said component moving relative to said guide in a releasing action as compared to said wedging action when said ram is moved in a direction opposite to said free fall.

14. The device according to claim 1 wherein a. said main valve is a duplex valve comprising a relatively small valve carried by, seated on and at least in part discharging into a relatively large valve having a stem;

b. said large valve is carried by and is afforded a sealing seat on a body removably secured to said cylinder head and wherein said stem has sliding support;

c. resilient means is interposed between said body and said small valve to urge the same to its seat on said large valve and in continuation of said urging to move said large valve to its seat on said body.

15. The device according to claim 1 including a piston packing assembly subject to fluid pressure and arranged for sliding engagement with the inner surface of the cylinder comprising an elastomeric member carried on said piston and being radially expandable under influence of fluid pressure.

16. The device according to claim 1 including a piston and packing assembly subject to fluid pressure and arranged for sealing sliding engagement with the inner surface of a cylinder and comprising a. a piston having a minor diameter and a major diameter spaced axially and radially from each other and having a shoulder extending axially in the direction of said pressure and radially from said minor diameter to said major diameter; an elastomeric piston packing carried on said piston and so positioned and proportioned as to have resilient sealing contact with said minor diameter and said inner surface;

an at least slightly flexible wear ring situated on said minor diameter and axially located between said packing and said shoulder whereby said wear ring is urged to said shoulder and is subject to radially expansive force affording radial pressure between said ring and said inner surface whereby it serves to centralize said piston within said cylinder and keep it out of contact with said inner surface while simultaneously serving as an obturator to prevent extrusion of said elastomeric piston packing along said inner surface.

17. The device according to claim 16 wherein said wear ring is proportioned on at least a portion of its inner diameter to ofier efiective resistance to extrusion of said packing between said ring and said minor diameter.

18. The device according to claim 17 wherein said wear ring has cooperating engagement on its upper surface with a separate ring having a close fit on said minor diameter and being proportioned and positioned to substantially prevent extrusion of said packing between said wear ring and said minor diameter.

19. The device according to claim 16 having a piston and packing assembly subject to fluid pressure and arranged for sliding sealing contact with the inner surface of a cylinder, said assembly comprising a. a piston having a major and a minor diameter and a shoulder extending radially from one to the other;

b. an elastomeric piston packing carried by said piston and so proportioned and positioned as to have resilient sealing contact with said minor diameter and said inner surface;

c. an at least slightly flexible wear ring situate on said piston between said packing and said shoulder and radially separated from said minor diameter by an elastomeric back-up ring;

the whole being characterized by said packing when under fluid pressure exerting an axially directed force on said backup ring which by virtue of its being confined between said shoulder and said packing expands radially and exerts an expansive force on said ring in a radial direction and urges it into intimate contact with said inner surface.

20. The device according to claim 17 wherein said wear ring is initially at least equal in diameter to the inside diameter of said cylinder.

21. The device according to claim 17 wherein said piston has a plurality of packings having sealing engagement with said piston and the inner surface of its cooperating cylinder and said packings are spaced axially along said piston, and

wherein a vent is provided affording passage in one direction for fluid in the space between adjacent packings to the cavity in said cylinder above said piston and wherein valve means close said vent to the flow of fluid in the reverse of said one direction. 

1. A thrust producing unit of the class described arranged and adapted for attachment to and removal from a support as an entity, said unit having a hollow housing containing at least in part: a. a reseRvoir for operating fluid; b. a cylinder head; c. a pair of cylinders of dissimilar diameter each having one end in sealed engagement with said head at one side thereof; d. a thrusting ram secured at one end to a piston slidable in the larger of said cylinders; e. a guide affording sliding support to said ram at a point remote from said piston; f. power transmission means for transmitting energy from without said housing to impose a reciprocative force on said ram and being movable relative thereto by reaction to said force in the direction opposite thereto; g. a pump comprising the smaller of said cylinders and a piston movable therein by movement of said transmission means to affect a flow of fluid from said reservoir to the larger of said cylinders and impose a thrusting effort on said piston therein and thence to said ram; h. pumping valve means comprising an inlet valve and a delivery valve for controlling said flow; i. main valve means comprising a main valve seatable by fluid pressure and openable by suction to permit the flow of fluid into said larger cylinder from said reservoir and a spring biasing said main valve against the urging of suction; j. releasable restraining means interposed between said housing and said transmission means to permit only limited movement thereof relative to said housing prior to release by said restraining means and permitting further movement thereof after release thereby, said release being automatically affected when said reaction to said force reaches a predetermined value; k. valve actuating means operable by movement of said transmission means to open said main valve aginst pressure and thereby permit the flow of fluid from said larger cylinder to said reservoir said actuating means comprising
 1. a first link having a portion engageable with said main valve,
 2. connecting means engaging said link and said transmission means and so proportioned that movement of said transmission means in one direction while within the range of said limited movement will cause said main valve to be opened while movement in the reverse direction within said range will permit said main valve to be closed,
 3. a second link arranged to engage and move said connecting means in a valve opening direction only and having a portion extending into the path of said first mentioned piston for engagement thereby when near the extreme limit of its excursion away from said cylinder head whereby movement of said first mentioned piston beyond said point will cause fluid pressure thereon to be relieved by the opening of said valve; l. a cylinder carrier supported by an inner surface of said housing and having supporting engagement with said cylinders; m. a cylinder head retainer arranged and adapted to urge said cylinder head and said cylinders toward said carrier and to transmit hydraulically imposed thrust to said housing, said unit being characterized in that said transmission means may impart a direct mechanical thrust on said ram and by simultaneous reactive movement, may also by means of said pump and said first mentioned piston impose a hydraulic thrust on said ram.
 2. connecting means engaging said link and said transmission means and so proportioned that movement of said transmission means in one direction while within the range of said limited movement will cause said main valve to be opened while movement in the reverse direction within said range will permit said main valve to be closed,
 2. The device according to claim 1 in which said housing comprises a tube having a configuration engageable by a mating configuration on a support for said unit, whereby reaction to thrust imposed by said ram on said support may be transmitted to said support.
 3. The device according to claim 2 wherein said cylinder head retainer comprises a sleeve engaged with a surface of said tube and which in conjunction with said cylinder head comprises said reservoir.
 3. a second link arranged to engage and move said connecting means in a valve opening direction only and having a portion extending into the path of said first mentioned piston for engagement thereby when near the extreme limit of its excursion away from said cylinder head whereby movement of said first mentioned piston beyond said point will cause fluid pressure thereon to be relieved by the opening of said valve; l. a cylinder carrier supported by an inner surface of said housing and having supporting engagement with said cylinders; m. a cylinder head retainer arranged and adapted to urge said cylinder head and said cylinders toward said carrier and to transmit hydraulically imposed thrust to said housing, said unit being characterized in that said transmission means may impart a direct mechanical thrust on said ram and by simultaneous reactive movement, may also by means of said pump and said first mentioned piston impose a hydraulic thrust on said ram.
 4. The combination of a device according to claim 2 and a support therefor, said support comprising a thrust opposing surface and a unit carrying portion having a configuration for mating with said configuration on said unit.
 5. The device according to claim 1 wherein said pumping valve means comprises a unit attached to said cylinder Head and situated within said reservoir.
 6. The device according to claim 1 wherein said main valve means comprises a unit attached to said cylinder head and located within said reservoir.
 7. The device according to claim 1 which further comprises a pressure limiting valve means arranged and adapted to limit the hydraulic pressure that may be developed by said pump and thereby limit the thrust that may be imposed on said ram.
 8. The device according to claim 7 wherein said pressure limiting valve means comprises a pressure limit adjusting means having a movable part movable to a desired setting from a point without said thrusting unit.
 9. The device according to claim 8 wherein said pressure limiting valve means further comprises a support for said movable part of said adjusting means and said adjusting means further comprises a portion for imposing the bias of a resilient member on to a valve openable by hydraulic pressure for pressing said valve to a closed position on a seat until said hydraulic pressure reaches a predetermined value.
 10. The device according to claim 9 wherein said movable part comprises a portion shaped for manipulation and which further comprises a screw threaded member rotatable by said portion shaped for manipulation and arranged to vary the bias imposed by said resilient means according to said predetermined value.
 11. The device according to claim 10 wherein a. a cover carried on said pumping valve means has an orifice communicating with a fluid conducting passage therein and affording said valve seat; b. a link movably attached to said cover affords said portion for imposing said bias and engages said resilient means to receive the bias thereof for urging said valve to a closed position on said seat; c. a closure for said reservoir affords said support and has markings indicative of predetermined values relative to which said protion shaped for manipulation may be indicatingly moved; d. said screw threaded member engages said cover, affords a reaction point for the bias of said resilient member, affords a frictional bearing surface and has an interlocking engagement with said portion shaped for manipulation arranged and adapted to permit said closure and said last mentioned portion to be removed from said unit and said screw threaded member and to be replaced thereon without falsification of the value of said markings.
 12. The device according to claim 1 wherein said releasable restraining means comprises a latch finger which a. is carried in movable relationship by said guide; b. affords its latching function within said housing; c. is accessible from without said housing for non-automatic unlatching manipulation.
 13. The device according to claim 1 comprising a friction creating component carried by said guide; and arranged to impose a frictional force on said ram by virtue of a wedging action between said guide and said ram, to prevent free fall thereof, said component moving relative to said guide in a releasing action as compared to said wedging action when said ram is moved in a direction opposite to said free fall.
 14. The device according to claim 1 wherein a. said main valve is a duplex valve comprising a relatively small valve carried by, seated on and at least in part discharging into a relatively large valve having a stem; b. said large valve is carried by and is afforded a sealing seat on a body removably secured to said cylinder head and wherein said stem has sliding support; c. resilient means is interposed between said body and said small valve to urge the same to its seat on said large valve and in continuation of said urging to move said large valve to its seat on said body.
 15. The device according to claim 1 including a piston packing assembly subject to fluid pressure and arranged for sliding engagement with the inner surface of the cylinder comprising an elastomeric member carried on said piston and being radially expandable under influence of fluId pressure.
 16. The device according to claim 1 including a piston and packing assembly subject to fluid pressure and arranged for sealing sliding engagement with the inner surface of a cylinder and comprising a. a piston having a minor diameter and a major diameter spaced axially and radially from each other and having a shoulder extending axially in the direction of said pressure and radially from said minor diameter to said major diameter; b. an elastomeric piston packing carried on said piston and so positioned and proportioned as to have resilient sealing contact with said minor diameter and said inner surface; c. an at least slightly flexible wear ring situated on said minor diameter and axially located between said packing and said shoulder whereby said wear ring is urged to said shoulder and is subject to radially expansive force affording radial pressure between said ring and said inner surface whereby it serves to centralize said piston within said cylinder and keep it out of contact with said inner surface while simultaneously serving as an obturator to prevent extrusion of said elastomeric piston packing along said inner surface.
 17. The device according to claim 16 wherein said wear ring is proportioned on at least a portion of its inner diameter to offer effective resistance to extrusion of said packing between said ring and said minor diameter.
 18. The device according to claim 17 wherein said wear ring has cooperating engagement on its upper surface with a separate ring having a close fit on said minor diameter and being proportioned and positioned to substantially prevent extrusion of said packing between said wear ring and said minor diameter.
 19. The device according to claim 16 having a piston and packing assembly subject to fluid pressure and arranged for sliding sealing contact with the inner surface of a cylinder, said assembly comprising a. a piston having a major and a minor diameter and a shoulder extending radially from one to the other; b. an elastomeric piston packing carried by said piston and so proportioned and positioned as to have resilient sealing contact with said minor diameter and said inner surface; c. an at least slightly flexible wear ring situate on said piston between said packing and said shoulder and radially separated from said minor diameter by an elastomeric back-up ring; the whole being characterized by said packing when under fluid pressure exerting an axially directed force on said back-up ring which by virtue of its being confined between said shoulder and said packing expands radially and exerts an expansive force on said ring in a radial direction and urges it into intimate contact with said inner surface.
 20. The device according to claim 17 wherein said wear ring is initially at least equal in diameter to the inside diameter of said cylinder.
 21. The device according to claim 17 wherein said piston has a plurality of packings having sealing engagement with said piston and the inner surface of its cooperating cylinder and said packings are spaced axially along said piston, and wherein a vent is provided affording passage in one direction for fluid in the space between adjacent packings to the cavity in said cylinder above said piston and wherein valve means close said vent to the flow of fluid in the reverse of said one direction. 